It states up in the top right that it's the mission that includes the SWAT attire, police car and weapon, rather than being extras for your wardrobe and garage.

That said, I've flagged this to our Production team who are going to investigate this and see if we can alter this functionality in a future title update so that when you finish the mission, you still have access to the car in your garage and the outfit in your wardrobe.

Just to manage your expectations, there's no timings for this right now - rest assured, though, if this were to happen I'll let you all know as soon as I receive an update."